The oscillometric method, the Korotkoff method, and the like, for example, are known as blood pressure measurement methods. The amplitude of a pulse wave measured at an upper arm changes according to the pressure being applied to the upper arm while the internal pressure of a cuff is being changed. In the oscillometric method, a blood pressure in the course of heart contraction (systolic blood pressure) and a blood pressure in the course of heart expansion (diastolic blood pressure) are measured on the basis of the amplitude. Systolic blood pressure is also referred to as maximum blood pressure and hereinafter referred to as SBP. SBP stands for systolic-blood-pressure. Meanwhile, diastolic blood pressure is also referred to as minimum blood pressure and hereinafter referred to as DBP. DBP stands for diastolic-blood-pressure.
In the Korotkoff method, in accordance with a pressure is applied to an upper arm while the internal pressure of a cuff is being changed, Korotkoff sounds are generated in the pressurized artery, and the blood pressure is measured on the basis of the generation of the Korotkoff sounds. In particular, a kind of Korotkoff method in which a detector, such as a microphone, detects Korotkoff sounds are also called microphone method.
In a situation that includes, for example, body movement of a subject to be measured, external vibrations, or noise from a surrounding area, a blood pressure measurement device based on the oscillometric method or the Korotkoff method detects the noise or the like in addition to blood pressure. As a result, a signal measured by the blood pressure measurement device contains large noise. Accordingly, it is difficult to properly measure a systolic blood pressure and a diastolic blood pressure on the basis of such a signal measured by the blood pressure measurement device. In other words, to properly measure blood pressure by the use of the blood pressure measurement device, it is necessary to induce the subject to be measured to be in a rest state or to create a quiet environment.
The sphygmomanometer (blood pressure measurement device) disclosed in PTL 1 includes a blood pressure measurement means for measuring blood pressure of a subject to be measured, and a rest state inducing means for inducing the subject to be in a rest state on the basis of the breathing state of the subject to be measured. The rest state inducing means applies microwaves to the subject to be measured.
The microwaves reflected from the subject to be measured undergo the Doppler shift due to a respiratory motion of the subject to be measured. The rest state inducing means calculates an actual expiration time and an actual inspiration time of the subject to be measured on the basis of the applied microwaves and the reflected microwaves, and induces the subject to be measured to a rest state on the basis of the ratio, total time or duration time of the expiration and inspiration times of the subject.
As described above, the blood pressure measurement device measures a pulse wave (pulse) containing noise in response to the subject to be measured coming in contact with a measurement region (specific region) used by the sphygmomanometer or the body movement of the subject to be measured.
PTL 2 discloses a non-invasive blood pressure measurement device capable of removing the noise and also relieving burden on a subject to be measured. The blood pressure measurement device has the function of removing noise from a measured pulse wave.
The blood pressure measurement device includes a cuff that measures, as a pulse wave, heartbeats at a body surface of the subject to be measured, multiple independent air bladders that set a uniform pressure condition for the cuff, and multiple pressure sensors each of which detects a pulse wave from a corresponding one of the air bladders. Each air bladder is connected to the corresponding one of the pressure sensors. The blood pressure measurement device also includes an arithmetic processing means for removing noise from the pulse waves measured by the pressure sensors by applying calculation according to a separation matrix method, adaptive filtering method, or both methods to the pulse waves.
The automatic blood pressure measurement device disclosed in PTL 3 properly measures a maximum blood pressure on the basis of a calculated amplitude ratio calculated using three expansion bags. The electronic sphygmomanometer disclosed in PTL 4 extracts a pulse wave while the internal pressure of a cuff is being reduced, and calculates the amplitude of the extracted pulse wave. The electronic sphygmomanometer determines whether the internal pressure of the cuff is insufficient, on the basis of whether the calculated amplitude is equal to or smaller than a threshold value. The blood pressure measurement device disclosed in PTL 5 measures pulse waves with multiple pulse wave sensors and calculates the time point at which the pulse wave having the largest amplitude among the measured pulse waves started. The blood pressure measurement device calculates the internal pressure of the cuff at the time point thus calculated, as a maximum blood pressure.